Cyanidation

About one hundred years ago, the introduction of the cyanidation revolutionized the treatment of the minerals of gold and silver. In the present time it continues being the preferred method of treatment for the great technical-economical advantages which it presents. It is worth taking into notice, that, if not all the minerals are directly cyanidable and for these there exist various alternatives which we will mention further ahead of this reading.

Classic Scheme for Minerals In High Law
 The classic scheme for the cyanidation of minerals of high law is mentioned as follows:

• Conminuition; which includes: crushing, grinding and classification.
• The adding of lime to obtain a pH between 10 and 11, as a protection to avoid the production of HCN.
• The adding of cyanide and lixiviation in a series of pachucas or mechanical aired agitators by draft tube, with time of residence of 12 to 48 hours. 
• Thickening of the lixiviated pulp and washing of the solids in countercurrent in thickeners or in in cyclones.
• Filtration, clarification and deairation to remove the solids in suspension and dissolved oxygen.
• Adding of zinc powder to precipitate the gold and silver for cementation.
• Refiltering of the solution through a pressing filter or Stellar.
• Return of the wasted solution to the circuit of washing in countercurrent.
• Fusion and Refining of the precipitate.

This flowsheet, used for quite some time in many countries is very simple and tested, but many minerals do not work sufficiently well in it, be it by low recuperations, contamination of the rich sollutions with impurities or low global efficiencies of the process. One of the problems is the presence of solids in suspension in the rich sollution, another is that this one is not sufficiently disaired and another, very common, the low efficiency by coprecipitation of other dissolved elements.

 Nevertheless, we can mention some recent developments of this technology, as, for example, South African operations which use the classic scheme advantageously, which instead of using the conventional Stellar filters, of high costs, the type of classifiers of cones.

These are capable of lowering the solids which are in uspentions of 400 ppm to 5 ppm in its latest versions (double V cones). The precipitation with Zn is recommended for high reasons Ag/Au and in small operations.